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1 July 2010 Passive Sperm Loss and Patterns of Sperm Precedence in Muscovy Ducks (Cairina moschata)
Sarah M. Stai, William A. Searcy
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We investigated the importance of passive sperm loss in the outcome of sperm competition in captive, wild-type Muscovy Ducks (Cairina moschata). In nature, Muscovy Ducks can be expected to experience more intense sperm competition than most other waterfowl because of their non-monogamous mating system. We estimated the instantaneous rate of sperm loss from the reproductive tracts of female Muscovy Ducks as 0.0235 ± 0.0018 h-1 [SE], a fairly typical rate in comparison to the few other species of birds in which passive sperm loss has been measured. We also measured sperm precedence in trials in which a captive female was allowed to mate with two males in succession, with either a 24-h or a 72-h lag between matings. Paternity was determined with microsatellite markers. The mean proportion of a female's eggs fertilized by the second male (P2) was 0.72 ± 0.14 in trials with the 24-h lag and 0.42 ± 0.13 in trials with the 72-h lag. The last-male precedence observed in the 24-h trials can be explained by a quantitative model in which passive sperm loss alone determines average success, but this model is not consistent with the outcome of the 72-h trials. Other factors, including perhaps postcopulatory female choice, must be acting in addition to passive sperm loss in the trials with the longer lag.

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Sarah M. Stai and William A. Searcy "Passive Sperm Loss and Patterns of Sperm Precedence in Muscovy Ducks (Cairina moschata)," The Auk 127(3), 495-502, (1 July 2010).
Received: 18 August 2009; Accepted: 1 January 2010; Published: 1 July 2010

Cairina moschata
Muscovy ducks
passive sperm loss
sperm competition
sperm precedence
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